Process for the production of a carbodiimide

Abstract

A process for the production of a carbodiimide, comprising the steps of: (1) reacting an amine represented by the following formula (A) with carbon disulfide in the presence of a catalyst at a reaction temperature of 50 to 150° C. to obtain a thiourea represented by the following formula (B): (In the above formula (A), R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) (In the above formula (B), R is as defined in the above formula (A); (2) desulfurizing the obtained thiourea with a hypochlorite in the presence of a basic compound to obtain a carbodiimide represented by the following formula (C): (In the above formula (C), R is as defined in the above formula (A)); and (3) purifying the obtained carbodiimide.

The invention claimed is: 
     
       1. A process for a production of a carbodiimide, comprising steps of:
 (1) reacting an amine represented by the following formula (A) with carbon disulfide in the presence of a catalyst at a reaction temperature of 50 to 150° C. to obtain a thiourea represented by the following formula (B): 
 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (A), R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (B), R is as defined in the above formula (A);
 (2) desulfurizing the obtained thiourea with a hypochlorite in the presence of a basic compound to obtain a carbodiimide represented by the following formula (C): 
 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (C), R is as defined in the above formula (A); and
 (3) purifying the obtained carbodiimide; 
 wherein the step (1) is carried out in a sealed condition. 
 
     
     
       2. The production process according to  claim 1 , wherein the step (1) is carried out in the presence of a hydrogen sulfide capture agent. 
     
     
       3. The production process according to  claim 1 , wherein the catalyst used in the step (1) is a compound having basicity with a pKa of its conjugate acid of 5 or more. 
     
     
       4. The production process according to  claim 3 , wherein the compound having basicity with a pKa of its conjugate acid of 5 or more is a substituted tertiary amine, a substituted imine, a substituted amide or a substituted heterocyclic ring. 
     
     
       5. The production process according to  claim 1 , wherein a phase transfer catalyst represented by the following formula (i) is further used in the step (2): 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (i), R1 to R4 are each independently a group selected from an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms and an aralkyl group having 7 to 20 carbon atoms, and A −  is a halogen anion. 
     
     
       6. The production process according to  claim 1 , wherein the hypochlorite used in the step (2) is sodium hypochlorite. 
     
     
       7. The production process according to  claim 1 , wherein the basic compound in the step (2) is sodium hydroxide, potassium hydroxide or a mixture thereof. 
     
     
       8. The production process according to  claim 1 , wherein the purification of the step (3) is recrystallization or extraction. 
     
     
       9. The production process according to  claim 1  comprising the following steps before the step (1):
 (α) reacting a compound represented by the following formula (a) with a compound represented by the following formula (b) in the presence of a phase transfer catalyst and an aqueous solution of an alkali metal hydroxide to obtain a nitro represented by the following formula (c): 
 
       
         
           
           
               
               
           
         
         wherein in the above formula (a), R is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and X is a halogen atom or a nitro group; 
       
       
         
           
           
               
               
           
         
       
       wherein in the above formula (c), R is as defined in the above formula (a); and
 (β) reducing the obtained nitro represented by the formula (c) to obtain an amine represented by the following formula (A): 
 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (A), R is as defined in the above formula (a). 
     
     
       10. The production process according to  claim 9 , where the phase transfer catalyst is a compound represented by the following formula (i): 
       
         
           
           
               
               
           
         
       
       wherein in the above formula (i), R1 to R4 are each independently a group selected from an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms and an aralkyl group having 7 to 20 carbon atoms, and A −  is a halogen anion. 
     
     
       11. The production process according to  claim 9 , wherein the phase transfer catalyst is at least one compound selected from the group consisting of tetraethylammonium salts, tetrabutylammonium salts, trioctylmethylammonium salts, benzyldimethyloctadecylammonium salts, benzyltriethylammonium salts, benzyltrimethylammonium salts and benzyltributylammonium salts. 
     
     
       12. The production process according to  claim 9 , wherein the aqueous solution of an alkali metal hydroxide is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.